1. Field of the Invention
This invention relates to a discharge tube lighting device for lighting a discharge tube, especially a fluorescent discharge tube. More particularly, this invention relates to a discharge tube lighting device which is capable of not only lighting highly efficiently fluorescent discharge tubes of a rich variety of kinds but also allowing adjustment of light over a wide range and which, when used in a system composed of a multiplicity of fluorescent discharge tubes, enables the individual fluorescent discharge tubes to be sequentially lighted.
2. Description of the Prior Art
Generally for the purpose of lighting a fluorescent discharge tube, there is required a lighting device which is vested with a function to apply to the opposite terminals of the fluorescent discharge tube a voltage exceeding the continuous discharge voltage of the fluorescent discharge tube at the time that the discharge is to be started and a function to regulate an electric current flowing through the fluorescent discharge tube and, at the same time, stabilize an electric current flowing in for checking fluctuation of voltage of the power source after the fluorescent discharge tube is turned off because the fluorescent discharge tube possesses a property of failing to effect desired start of the discharge unless a voltage several times the continuous discharge voltage is applied at the time that the discharge is to be started and, on the other hand, a negative property of keeping at a fixed magnitude the opposite-terminal voltage in spite of an increase in the feed current during the continuous discharge.
Most, if not all, lighting devices which are utilized most popularly today make direct use of a commercial-frequency power source. Their operating principle resides in lighting a fluorescent discharge tube of a small capacity by means of a glow tube and a choke coil (stabilizer) or lighting a fluorescent discharge tube of a medium or large capacity instantaneously by means of a stabilizer fitted with a special winding capable of functioning as a heater circuit and a high-voltage circuit. Very recently, a lighting device which is composed of electronic circuits and enabled to light a fluorescent discharge tube with the high-frequency voltage emitted from the electronic circuits as disclosed in Japanese Utility Model Application Disclosure SHO 63(1988)-18,797 has been gaining in popularity. The conventional lighting device of a small capacity, because of the principle that the lighting relies on the action of a glow tube, necessitates a choke coil of a relatively large capacity and renders a dimensional reduction extremely difficult. The conventional lighting device of a medium or large capacity, for the same reason as given above, renders it extremely difficult to attain a dimensional reduction. An attempt at imparting an advanced function such as adjustment of light to the conventional lighting device is impracticable by reason of the characteristic inherent in the construction of the device. It has been difficult, therefore, for the conventional lighting device to light a fluorescent discharge tube more efficiently through adjustment of light. The lighting device composed of electronic circuits as described above is capable of effecting such adjustment of light as described above to some extent. Any attempt at enabling a sole lighting device to attain stable adjustment of light in a wide range and, at the same time, effect highly efficient lighting of a fluorescent discharge tube is realized only to a limited extent. Further, the conventional lighting devices are such that they are used exclusively for fluorescent discharge tubes of severally proper ratings. Where the production is contemplated on a commercial scale, therefore, it has been necessary to produce lighting devices of numerous types fitting various kinds and capacities of fluorescent discharge tubes marketed, such as lighting devices adapted exclusively for 40-W straight-tube type fluorescent discharge tubes and lighting devices adapted exclusively for 20-W circle-type fluorescent discharge tubes, for example. For simultaneous lighting of a plurality of fluorescent discharge tubes by the use of conventional lighting devices, it is necessary either to furnish the fluorescent discharge tubes one each with lighting devices or to provide them with a power source and a rectifying circuit both large in size and capacity enough to attain simultaneous lighting of the plurality of fluorescent discharge tubes. The lighting devices, therefore, suffer from dimensional augmentation and entail an addition to power consumption and prove to be highly disadvantageous in terms of weight, volume, cost, and power consumption, for example. Moreover, the rush current of high amperage which occurs at the time of lighting such fluorescent discharge tubes brings about an adverse effect on internal circuit elements. In the worse case, the adverse effect may amount to destruction or serious damage to the circuit elements.